Programmed cell death (apoptosis) plays an essential role in many processes underlying embryological development, from formation of the digits to selection of effective immunological repertoires in Iymphocytes. It is generally believed that loss of normal onset of apoptosis is involved in the etiology of many cancers. Increased understanding of the signaling components within cells that control this process may lead to improved treatments for cancer. The applicant has identified a critical role in early embryogenesis for the Calcium Modulating cyclophilin Ligand (CAML). CAML is an integral membrane protein localized at internal Ca2+ containing vesicles, and appears able to cause release of intracellular Ca2+ stores when stimulated by physical interaction with cell surface receptors. Genetic knockout of the CAML gene in mice causes a block in embryonic development between 4.5 and 6.5 days post coitum. Remarkably, embryoid bodies derived from CAML-/- ES cells fail to develop a 'proamniotic cavity," a structure shown by others to arise upon induction of programmed cell death in a specific area of the inner cell mass. An attractive hypothesis is that CAML activates a developmentally important programmed cell death pathway via its ability to release intracellular Ca2+ stores. The overall goal of this project is to determine how, at the molecular level, the CAML protein regulates early embryogenesis and lymphopoiesis in the mouse. Experiments will focus on determining the mechanism of action of CAML, by identifying its functional domains, and identifying protein contacts that mediate its action. Chimeric experiments in mice will allow the identification of other developmental steps that require CAML function. In vitro experiments examining the function of CAML in embryoid body formation will further delineate its mechanism of action in contributing to apoptosis. Lastly, the role of CAML in development and function of Iymphocytes will be determined in chimeric mice.